The feeding mechanisms of the Daphniidae (Crustacea: Cladocera): recent suggestions and neglected considerations

While the importance of grazing by anomopod cladocerans of thefamily Daphniidae on crops of planktonic algae and bacteria,and on detritus, is widely recognized, and although many calculationshave been made on the filtering rate of these crustaceans, thefeeding mechanisms involved in these processes have frequendybeen misinterpreted by ecologists. Recent accounts that purportto describe the feeding mechanism of Daphnia are based on misinterpretationsof morphology and are completely erroneous. The ancestors ofdaphniids were probably benthic, littoral animals, similar invarious respects to primitive represcritatives of extant chydoridsand macrothricids. The feeding mechanisms of the latter giveuseful indications of the kind of device from which that ofthe daphniids probably arose. The daphniid mechanism was derivedby restricting particle abstraction to trunk limbs 3 and 4.Contraiy to recent claims, mink limbs 1 and 2 are not involvedin this element of the feeding process. Comparative studieson many anomopods reveal invariable correlations. Species employingcurrents to cany food particles have filter plates bearing filtratorysetules. Species that, for whatever reason, do not employ currents,except sometimes for respiration, have homologous structuresthat lack filtratory setules, even when, as is often the case,they feed on particulate matter. Comparisons with other branchiopodsare also helpful.